The role of a small molecular dipole moment for efficient non-doped deep blue thermally activated delayed fluorescence emitters

Abstract

Non-doped and solution-processable deep blue emitters can greatly reduce the manufacturing cost of organic light-emitting diodes (OLEDs). However, influences of parameters concerning intermolecular interactions in solid state have not yet been explored. Herein, we proposed molecular dipole moment as a pre-experimental parameter to evaluate an emitter’s performance in the solid state. By extracting efficiency data of OLEDs based on blue-emitting molecules from literature and calculating the dipole moments of these molecules, we found a clear inverse relationship. Three deep blue TADF emitters with similar molecular emitting properties were designed and synthesized. The PL efficiency of their solid films and device performance was found to decrease as the molecular dipole increased. Specifically, TDBA-SPQ with the smallest dipole moments of 1.86 D delivered much better performance in both vacuum-processed and solution-processed non-doped OLEDs with record-high EQEmax of 22.7% and 15.2% with CIE-y coordinates of 0.136 and 0.123, respectively.